The present invention relates to a signal editing and processing apparatus for converting a plurality of continuous signals to a transmitting signal in which a pause period and a signal transmission period having an integer period ratio with said pause period are sequentially repeated. This invention is widely related to a signal transmission system wherein the continuous signals are transmitted through an intermittent transmission line which is interrupted time-sequentially.
Especially, this invention provides an editing and processing apparatus for an audio signal in a still picture transmission system for alternately transmitting video and PCM audio signals which are intermittently divided by different periods of division, without losing continuity of the audio signal.
As to a signal which is divided by a given constant period, a television audio signal or a facsimile signal which is divided by the period of scanning, and a TDM signal obtained by time-divisionally multiplexing audio and other information signals in the form of pulse code modulation (PCM) signal are known.
A type of broadcasting which is able to conform with the needs of the variety and individuality of human life can be considered one of the ideals of future broadcasting. Super multiplexing still picture broadcasting elicits great interest of broadcasters and educators as an economical and technological means through which a great deal of information can be conveyed.
The concept of still picture transmission by television signals has been reported by W. H. Huges et al., at Oklahoma State University. This system has been planned for a cable transmission system which is capable of two-way transmission. But, they did not report the details of sound transmission. In most cases, it is advantageous to transmit the sound together with the picture because, in general, watching television without sound does not use the human senses well, and it is less effective for viewers. Therefore, it has been desired to develop a novel transmission system of still pictures and corresponding sounds in order to study the most effective use of still picture broadcasting and the acceptability of still pictures by viewers.
The present invention is to provide a signal editing and processing apparatus in a transmission system which can transmit still pictures together with sounds related thereto. It should be noted that the present invention is not limited to a transmission system for still pictures and their related sounds, but may be used to transmit television video signals or facsimile signals which are divided into scanning periods and any other time division multiplexed information signals in the form of PCM, PTM (pulse time modulation), PWM (pulse width modulation) or PAM (pulse amplitude modulation) signals. However, for the sake of explanation, in the following description the transmission system for transmitting still pictures and related sounds as television signals through a television transmitting path will be explained. That is to say, video signals of still pictures and audio PCM signals are transmitted on the same transmission path at a rate of one to two television frames of the NTSC system. Thus, video signals of each still picture are transmitted in one frame period (about 1/30 seconds) as quasi-NTSC signals and audio PCM signals are transmitted in successive two frame periods (about 1/15 seconds). A plurality of still pictures and their related sounds constitute a single group termed as a program. At a transmitter end, this program is transmitted repeatedly and at a receiver end one can select a desired still picture and its related sound from the source program to be transmitted. At the transmitter end there may be provided a plurality of programs and a first program is transmitted repeatedly in a given period and so on. And at the receiver end one can select a desired program from a plurality of transmitted programs. A time duration of a program is established considering various factors such as amounts of information to be transmitted, i.e., the number of still pictures, necessary time duration of sounds, etc., property of a transmission path and its bandwidth, complexity of apparatuses at transmitter and receiver ends, and permissible access time (permissible waiting time) on the basis of psychological characteristic of viewers. In the embodiment described hereinafter a time duration of a program is determined to be 5 seconds.
Now, a basic construction of the still picture transmitting system described hereinabove will be firstly explained with reference to FIGS. 1 to 4. FIG. 1 shows a format of the video-audio muliplexed signal to be transmitted. FIG. 1a denotes a program of five seconds. The program is termed as a master frame MF. The master frame MF consists of five sub-frames SF, each of which has a duration of one second. As shown in FIG. 1b, each sub-frame SF consists of 10 video-audio frames VAF and each video-audio frame VAF has a duration of 1/10 seconds. As illustrated in FIG. 1c, each video-audio frame VAF further consists of a video frame VF of one television frame period (about 1/30 seconds) and an audio frame AF of two television frame periods (about 1/15 seconds). Each audio frame AF further consists of a first audio frame A.sub.1 F and a second audio frame A.sub.2 F, each having one television frame period (about 1/30 seconds). Thus, the master frame MF is composed of a 150 television frames.
By constructing the master frame MF as mentioned above, in the master frame MF, there may be inserted 50 still pictures. However, in fact, it is necessary to transmit code signals for identifying still pictures and their related sound and for indicating timings of starts and ends of various signals. It is advantageous to transmit such code signals in the video frames VF rather than in the audio frames AF. In the present embodiment, code signals are transmitted in a video frame VF of each sub-frame SF. A frame during which the code signals are transmitted is referred to as a code frame CF. FIG. 1d shows a part of the sub-frame SF which includes said code frame CF. Therefore, in the master frame MF, there are inserted 45 still pictures and thus, it is required to transmit 45 sounds related thereto, i.e., 45 channels of audio signals.
Sound like speech or music needs several seconds or more to give some meaning, because sound is inherently continuous. In the present embodiment an average duration of each sound relating to each still picture is limited to ten seconds. As mentioned above, the master frame MF has a duration of only 5 seconds, so that in order to transmit sounds of 10 seconds, it is necessary to use the number of channels twice the number of sound channels. That is, in order to transmit sounds of 45 channels relating to 45 still pictures, it is required to establish 90 audio channels. Moreover, it is impossible to transmit audio signals in the video frames VF. Therefore, PCM audio signals must be divided and allocated in the audio frames AF only. In order to effect such an allocation treatment for audio signals, the PCM audio signals of 90 channels are divided into two groups PCMI and PCMII as shown in FIG. 1e. Portions of PCMI corresponding to the second audio frames A.sub.2 F and the video frames VF are delayed for two television frame periods of about 1/15 seconds and portions of PCMII corresponding to the video frames VF and the first audio frames A.sub.1 F are delayed for one television frame period of about 1/30 seconds. PCM signals thus delayed form audio channels A and C are illustrated in FIG. 1e. Portions of PCMI and PCMII which correspond to the first audio frames A.sub.1 F and the second audio frames A.sub.2 F, respectively, are directly inserted in audio channels B.sub.1 and B.sub.2 to form an audio channel B. In this manner, in the audio channels A, B and C, there are formed vacant frames and these vacant frames correspond to the video frames VF. By effecting such an allocation for the audio signals, in each audio frame AF it is necessary to establish a number of audio channels which is one and a half times of the number of the audio signal channels. In the present embodiment, 135 audio channels have to be provided in each audio frame AF. In this manner, audio signals of 135 channels are inserted in each audio frame AF in the form of PCM signals allocated in given time slots.
An embodiment of a transmitting apparatus for effecting the above mentioned still picture-PCM audio signal time division multiplexing transmission will now be explained with reference to FIG. 2. The transmitting apparatus comprises a video signal processing system and an audio signal processing system. The video signal processing system comprises a random access slide projector 1, on which are loaded slides of still pictures to be transmitted. The projector 1 projects optically an image of a slide of a still picture onto a television camera 3. The camera 3 picks up the image and produces an electrical video signal. The video signal is supplied to a frequency-modulator 5 and frequency-modulates a carrier by the video signal. The FM video signal is amplified by a recording amplifier 7 and an amplified video signal is supplied to a video recording head 9. This head 9 is an air-bearing type floating head and is arranged to face a surface of a magnetic disc memory 11. The head 9 is driven by a head driving mechanism 13 so as to move linearly in a radial direction above the surface of the disc memory 11. The disc memory 11 is preferably made of a plastic disc having a coated magnetic layer thereon. This kind of memory has been described in detail in an NHK Laboratories Note Serial No. 148, "Plated magnetic disc using plastic base"; December 1971. The disc 11 is rotatably driven by a motor 15 at a rate of thirty rounds per second. There is further provided an air-bearing type floating head 17 for reproducing video signals recorded on the disc memory 11. The reproducing head 17 is also driven by a driving mechanism 19 so as to move linearly in a radial direction above the surface of the disc 11. The magnetic heads 9 and 17 are moved intermittently so that on the surface of the disc 11 there are formed many concentric circular tracks. On each track is recorded the video signal for one television frame period corresponding to each still picture. The reproduced video signal from the reproducing head 17 is supplied to a reproducing amplifier 21 and the amplified video signal is further supplied to a frequency-demodulator 23. The demodulated video signal from the frequency-demodulator 23 is supplied to a time-error compensator 25, in which time-errors of the demodulated video signal due to non-uniformity of rotation of the disc memory 11 can be compensated. The time-error compensator 25 may be a device which is sold from AMPEX Company under a trade name of AMTEC. The time-error compensated video signal is supplied to a video input terminal of a video-audio multiplexer 27.
The audio signal processing system comprises an audio tape recorder 29 of the remote controlled type. On this tape recorder 29 is loaded a tape on which many kinds of audio signals related to the 45 still pictures have been recorded. The reproduced audio signals from the tape recorder 20 are suplied to a switcher 31 which distributes each audio signal corresponding to each still picture to each pair of recording amplifiers 33-1, 33-2; 33-3, 33-4, . . . 33-n. The amplified audio signals from the amplifiers 33-1, 33-2, 33-3 . . 33-n are supplied to audio recording heads 35-1, 35-2, 35-3 . . . 35-n, respectively. There is provided an audio recording magnetic drum 37 which is rotated by a driving motor 39 at a rate of one revolution for 5 seconds. As already described above, each sound corresponding to each still picture lasts for 10 seconds, so that each audio signal of each sound is recorded on two tracks of the magnetic drum 37 by means of each pair of audio recording heads 35-1, 35-2; 35-3, 35-4, . . . 35-n. That is, a first half of a first audio signal for 5 seconds is recorded on a first track of the drum 37 by means of the first recording head 35-1 and then a second half of the first audio signal is recorded on a second track by means of the second head 35-2. In this manner, the successive audio signals corresponding to the successive still pictures are recorded on the magnetic drum 37.
The audio signals recorded on the drum 37 are simultaneously reproduced by audio reproducing heads 41-1, 41-2, 41-3 . . . 41-n, the number of which corresponds to the number of the audio recording heads 35-1, 35-2, . . . 35-n. In the present embodiment n=90. The reproduced auido signals are amplified by reproducing amplifiers 43-1, 43-2, 43-3 . . . 43-n. The amplified audio signals are supplied in parallel to a multiplexer 45 in which the audio signals are multiplexed in time division mode to form a time division multiplexed (TDM) audio signal. The TDM audio signal is then supplied to an A-D converter 47 to form a PCM-TDM audio signal. This PCM audio signal is further supplied to an audio allocation processor 49 in which the PCM audio signal is allocated in the audio frames AF as explained above with reference to FIG. 1e. The detailed construction and operation of the audio allocation processor 47 will be explained later. The PCM audio signal supplied from the processor 49 is a two-level PCM signal. This two-level PCM signal is converted in a two-four level converter 51 into a four-level PCM signal. The four-level PCM audio signal is supplied to an audio signal input terminal of the video-audio multiplexer 27. In the multiplexer 27, the video signal from the time-error compensator 25 and the four-level PCM audio signal from the two-four level converter 51 are multiplexed in a time division mode. A multiplexed video-audio signal from the multiplexer 27 is supplied to a code signal adder 53 which adds to said signal the code signal for selecting desired still pictures and their related sounds at a receiver end to form the signal train shown in FIG. 1d. The signal train from the code signal adder 53 is further supplied to a synchronizing signal adder 55 in which a digital synchronizing signal is added to form an output video-audio signal to be transmitted.
In the transmitting apparatus shown in FIG. 2, there are further provided servo amplifiers 57 and 59 so as to maintain the rotation of the video disc memory 11 and the audio magnetic drum 37 to be constant.
In order to transmit the output video-audio signal as a television signal, it is necessary to synchronize the operation of the various portions of the transmitting apparatus with an external synchronizing signal. To this end, there is further provided a synchronizing and timing signal generator 61 which receives the external synchronizing signal and generates synchronizing and timing signals R, S, T, U, V, W, X, Y and Z for the camera 3, the servo amplifiers 57 and 59, the time-error compensator 25, the audio multiplexer 45, the A-D converter 47, the audio allocation processor 49, the two-four level converter 51 and the synchronizing signal adder 55, respectively. The generator 61 further supplies synchronizing and timing signals to a control device 63 which controls selection of still pictures and sounds, recording, reproducing and erasing of video and audio signals, generation of a code signal; etc., the control device 63 further receives instruction signals from an instruction keyboad 65 and supplies control signals A, B, C, D, E, F and G to the projector 1, the audio tape recorder 29, the code signal adder 53, the video recording amplifier 7, the video recording head driving mchanism 13, the video reproducing head driving mechanism 19 and the switcher 31, respectively.
In the transmitting apparatus mentioned above, the random access slide projector 1 is controlled by the control device 63 to project successive by 45 still pictures and the video recording head 9 is driven by the mchanism 13 so as to face tracks of the disc memory 11. In this case, the video recording head 7 moves in one direction to face alternate by 23 tracks so as to record 23 still pictures and then moves in an opposite direction to face the remaining 22 tracks which are situated between the tracks on which the video signals of the first 23 still pictures have been recorded. The video recording amplifier 7 receives a gate signal D of 1/30 seconds from the control device 63 and supplies a recording current to the video recording head 9 for said period. The motor 15 for driving the disc 11 is controlled by the servo amplifier 57 to rotate at a constant angular velocity of 30 rps. The servo amplifier 57 detects the rotation of the disc 11 and controls the motor 15 in such a manner that the detected signal coincides with the timing signal S supplied from the generator 61. The video reproducing head 17 is driven by the mechanism 19 in the same manner as the video recording head 9. The reproducing head 17 is moved in the audio frame and code frame period and is stopped in the video frame period to reproduce the video signal. The reproducing head 17 repeatedly reproduces the audio signal of 45 still pictures.
As already explained, the audio signal of each sound relating to each still picture is recorded on two tracks of the magnetic drum 37. This drum 37 is driven by the motor 39 and this motor 39 is controlled by the servo amplifier 59. The servo amplifier 59 detects the rotation of the drum 37 and controls the motor 39 in such a manner that the detected signal coincides with the timing signal T supplied from the generator 61.
It is possible to revise a portion of the previously recorded pictures or sounds to new pictures or sounds while reproducing the remaining pictures and sounds. For picture information, the video recording head 9 is accessed to a given track by the head driving mechanism 13 and a new picture is projected by the random access slide projector 1 and picked up by the television camera 3. The video signal thus picked up is supplied to the frequency-modulator and then to the recording amplifier 7. Before recording, d.c. current is passed through the video recording head 9 and the previously recorded video signal is erased. Then the new video signal is recorded on the erased track of the disc 11. For sound information, a new sound is reproduced by the audio tape recorder 29 and a given track of the magnetic drum 37 is selected by the switcher 31. before recording, the selected track is erased by an erasing head (not shown) corresponding to the selected recording head. These operations are controlled by the control signals supplied from the control device 63 on the basis of the instruction from the instruction keyboard 65 and the timing signals from the generator 61.
Next, a basic construction of a receiver will be explained with reference to FIG. 3. A received signal is supplied in parallel to a synchronizing signal regenerator 67, a video selector 69 and an audio selector 71. In the synchronizing signal regenerator 67, a synchronizing signal is regenerated from the received signal. The synchronizing signal thus regenerated is supplied to a timing signal generator 73. The timing signal generator 73 is also connected to an intruction keyboard 75. The timing signal generator 73 produces timing signals to the video selector 69 and the audio selector 71 on the basis of the synchronizng signal from the regenerator 67 and the instruction from the keyboard 75. The video selector 69 selects a desired video signal and the audio selector 71 selects a desired audio signal related to the desired video signal. The selected video signal of the desired still picture is once stored in a one-frame memory 77, and the video signal of one frame period is repeatedly read out to form a continuous television video signal. This television video signal is displayed on a television receiver 79.
The selected audio PCM signal is supplied to an audio reallocation processor 81 to recover a continuous audio PCM signal. The audio PCM signal is supplied to a D-A converter 83 to form an analog audio signal. This audio signal is reproduced by a loud speaker 85.
Now, the operation of the receiver will be explained in detail with reference to FIG. 4 showing various waveforms.
In the synchronizing signal regenerator 67, PCM bit synchronizing signals and PCM frame synchronizing signals are reproduced in the manner which will be described later in detail and also gate signals shown in FIGS. 4b, 4c and 4d are produced. The timing signal generator 73 detects a picture identification code VID which has been transmitted in a vertical flyback blanking period at a foremost portion of the picture transmission frame period VF. As shown in FIG. 4a, the picture identification code .alpha. for the picture P.alpha., the picture identification code .beta. for the picture P.beta. and so on are transmitted at the foremost portion of the picture transmission frame periods VF. The timing signal generator 73 compares the detected picture identification code VID with a desired picture number, for example .beta. instructed by the keyboard 75. If they are identified to each other, the timing signal generator 73 produces a coincidence pulse shown in FIG. 4e. The coincidence pulse is prolonged by a monostable multivibrator circuit as shown by a dotted line in FIG. 4e and the prolonged pulse is gated out by the gate signal shown in FIG. 4b to form a video gate signal illustrated in FIG. 4f. The video gate signal is supplied to the video selector 69 to gate out the video signal P.beta. in a desired video frame and the video signal P.beta. thus selected is stored in the one-frame memory 77. In the memory 77, the video signal P.beta. is repeatedly read out so that the continuous video signal shown in FIG. 4g is supplied to the television receiver 79. Thus, the television receiver 79 displays the video signal P.beta. as a still picture instead of the picture P.eta. which has been displayed.
The audio signal is transmitted in the audio frame periods A.sub.1 F and A.sub.2 F in the form of a PCM multiplexed signal. The timing signal for selecting a PCM channel number corresponding to the desired picture number, for example .beta. is generated by counting the above mentioned PCM bit synchronizing pulses and PCM frame synchronizing pulses. The timing signal thus generated is supplied to the audio selector 71 to select the desired PCM signal related to the selected still picture. FIG. 4h illustrates a pulse series of the audio channel A selected by the audio selector 71 and FIG. 4i shows a pulse series of the audio channel B.sub.1 selected by the audio selector 71 and gated out by the gate signal shown in FIG. 4c. The audio reallocation processor 81 supplies the PCM pulse series shown in FIG. 4h directly to the D-A converter 83 and also supplies the PCM pulse series of FIG. 4i to the D-A converter 83, but after a delay of two television frame periods as shown in FIG. 4j. To this end, the timing signal from the generator 73 is supplied to the processor 81. The pulse series shown in FIGS. 4h and 4j are combined to form a continuous pulse series shown in FIG. 4k. The combined PCM signal is converted by the D-A converter 83 into the continuous analog audio signal.
When the desired sound is transmitted in the channels C and B.sub.2, the same operation as above will be carried out as shown in FIGS. 4l, 4m, 4n and 4o to form a desired continuous analogue audio signal. The picture number and the PCM channel number may be correlated to each other in such a manner that even number pictures correspond to the audio channels A and B.sub.1 and odd number pictures correspond to the audio channels C and B.sub.2.
As is apparent from the above, in case when the continuous signals are effectively transmitted through the intermittent transmission line such as transmitting the video signal of the still picture and the audio signal after multiplexing these signals, these plurality of signals are transmitted through a plurality of channels of the transmission line having the sequentially repeated periods composed of a pause period and a signal transmitting period having an integer ration therebetween. In this case, the respective ones of said plurality of channels of the continuous signals are divided into the first signal having a duration equal to that of said signal transmission period and the second signal having a duration equal to that of said pause period, one of said first and second signals being delayed, and only the second signals in said plurality of channels of the continuous signals being sequentially combined so as to form the third signal having a duration equal to that of said signal transmission period. After such a signal processing, the channel for transmitting said first signal and the further channel for transmitting the third signal are provided so as to transmit these first and third signals during the signal transmission period.
Next, the explanation will be made about the process for converting the plurality of channels of the continuous signals to the above-mentioned transmitting signals.
Referring to FIG. 5, an embodiment of the signal transmission system in which the ratio of the signal transmission period and the pause period is 2:1, such as a still picture transmission system in which the audio frame (AF) period is equal to two TV frames (2F) and the video frame (VF) period to one TV frame (1F) will be explained in detail hereinafter.
As shown in FIG. 5a, two channels of audio signals a.sub.1 and a.sub.2 are respectively divided into parts a.sub.1-1 and a.sub.2-1 corresponding to the VF period and parts a.sub.1-2 and a.sub.2-2 corresponding to the AF period. The parts a.sub.1-1 and a.sub.2-1 are delayed by 1F and 2F respectively. Both of the thus delayed parts a'.sub.1-1 and a'.sub.2-1 are time-sequentially combined to form a new signal B which is contained in No. 2 channel. The remaining parts a.sub.1-2 and a.sub.2-2 are contained respectively to No. 1 and No. 3 channels as signals A and C. In this manner, two kinds of sound signals having a time length of 3F are converted to three resultant signals contained in the channels of 2F.
In order to reproduce the original signals a.sub.1 and a.sub.2 from the resultant signals A, B and C of FIG. 5a at the receiving side, the process shown in FIG. 5b is employed. In this case, the amount or time length of the signal to be temporarily stored is 2F as is clear from FIG. 5b. Because, in the transmitting side, the 1F parts a.sub.1-1 and a.sub.2-1 are time-sequentially combined after being delayed or stored, it is necessary to store the received signals in order not to reverse the sequence of the received signals at the receiving side. In the usual broadcasting system, however, it is preferable to reverse the sequence of the signals to be temporarily stored in the transmitting side, since, in order to pervade the still picture broadcasting, it is desired to make simple the configuration of the receiving unit compared with the transmitting unit. That is, the time lengths of the parts a.sub.1-1 and a.sub.2-1 are 2F, respectively, and the time lengths of the parts a.sub.1-2 and a.sub.2-2 are 1F, respectively. As shown in FIG. 5c, the beginning instant of the audio signal a.sub.2 is delayed by a 1F period, and the part a.sub.1-1 is delayed by a 2F period so as to form a signal a'.sub.1-1 which is contained in the channel No. 1. The part a.sub.2-1 is delayed by a 1F period so as to form a signal a'.sub.2-1 which is contained in the channel No. 3. Both of the remaining parts a.sub.1-2 and a.sub.2-2 are combined so as to be contained in the channel No. 2. When reproducing, as shown in FIG. 5d, the parts a.sub.1-1 and a.sub.2-1 are not delayed, the part a'.sub.1-2 is delayed by the 2F period, and the part a'.sub.2-2 is delayed by the 1F period. The resultant signals after such delaying are combined with the parts a.sub.1-1 and a.sub.2-1 so as to reproduce the original signals a.sub.1 and a.sub.2. According to this processing, it is sufficient that the signal of the 1F period be stored by delay or storage means of the receiving unit, so that the arrangement of the receiving terminal becomes simple.
As clearly shown in FIGS. 5c and 5d, according to the above method, two signals a.sub.1 and a.sub.2 are divided into sections or parts such as a.sub.1-1, a.sub.1-2, a.sub.2-1, a.sub.2-2, the sequence of which is rearranged. In this case, the sequence of signals contained in each part is not changed, so that it is sufficient only to delay the signal by taking the time period of the part (1F) as the unit of delay time.
In this way, 96 kinds of audio signals are converted into 144 kinds of sectional signals each of which is contained in a time slot having a time duration of 2F. Between two adjacent time slots formed is a blank period of 1F. In order to multiplex these 144 kinds of signals, the original audio signal is modulated in the form of PCM and the signal obtained by this PCM signal is multiplexed in time division. Here, if the above signal delaying and combining is processed within a frequency band in which the original audio signal is present, then 96 independent audio processors are required for processing the above delay and combination of the signals.
In order to reduce the number of such independent audio processors, two PCM-TDM apparatuses are employed for processing 48 audio signals in a PCM-TDM manner. The two outputs resulting from these two apparatuses by PCM-TDM processing can be used as two channels of signals a.sub.1 and a.sub.2 of FIG. 5. These outputs can be dealt with only two PCM-TDM type audio processors in a same way as the above, so that the configuration of the audio processor in which the three signals A, B and C are multiplexed can be fabricated without complexity.
FIG. 6 shows an arrangement of an audio processor in the transmitting unit in the case of multiplexing audio signals in a PCM-TDM manner. This audio processor corresponds to said audio multiplexer 45, the A-D converter 47, the audio allocation processor 49 and the two-four level converter 51 in FIG. 2. In FIG. 6, the reference numeral 87 denotes a PCM timing signal generator for producing PCM frame synchronizing signal F, audio sampling signal S, bit clock bc, synchronizing signal V per TV frame and so on. The reference numeral 89 denotes a gate signal generator for producing gate pulses g.sub.1, g.sub.2, g.sub.3 and g.sub.4 from said synchronizing signal V from said generator 87. These gate pulses have such periods as shown in FIG. 4a. The reference numerals 91 and 93 denote PCM-TDM processors in which the audio signal is converted into the PCM signal and in which the PCM signal is multiplexed in time division. For example, 96 channels of audio signal are separated into two sets of channels, i.e., 1st to 48th channels and 49th to 96th channels. These two channel sets are processed to form PCM-TDM signals a.sub.1 and a.sub.2. The reference numerals 95, 97, 99 and 101 denote AND gate circuits. The gate 95 receives the a.sub.1 signal and gate signal g.sub.1 to gate said a.sub.1 signal as shown in FIG. 5c. That is, this gate is on during every two frame periods such as t.sub.0 -t.sub.2, t.sub.3 - t.sub.5 . . . and this gate is off during the remaining one frame period such as t.sub.2 -t.sub.3, t.sub.5 -t.sub.6 . . . The gate 97 receives the gate signal g.sub.2 the polarity of which signal is reversed to that of signal g.sub.1. This gate is off during two frame periods and is on during one frame period (such as t.sub.2 -t.sub.3). The gate 99 receives the gate signal g.sub.3. This gate signal g.sub.3 is delayed by one frame period relative to the gate signal g.sub.1, so that this gate 99 is on during two frame periods (such as t.sub.1 -t.sub.3) and is off during one frame period after one frame period compared with the gate 95. The gate 101 receives the gate signal g.sub.4 which is delayed by one frame period relative to the gate signal g.sub.2. This gate is off during two periods and is on during one period (such as t.sub.3 -t.sub. 4). These on and off timings are reversed to that of said gate 99. A delay circuit 103 is connected to said gate 95 to delay the output thereof by two frame periods. A delay circuit 105 is connected to said gate 101 to delay the output thereof by one frame period. The outputs of said gates 97 and 99 are connected to a mixing circuit 107. The reference numeral 109 denotes a time division multiplexer which receives the signal a'.sub.1-1 from the delay circuit 103, the signal a'.sub.2-1 from the delay circuit 105 and the signals a'.sub.1-2 , a'.sub.2-2 from said mixing circuit 107 so as to multiplex these signals in time division. The output of this multiplexer 109 is supplied to a two-four level converter 111 in which a two level PCM signal is converted to a four-level PCM signal as described hereinafter.
The multiplexer 109 is composed of a shift register such as "9300" of the Fairchild Company which has a plurality of parallel input terminals and one serial output terminal. Supplied to these parallel input terminals are said signals a'.sub.1-1 , a'.sub.1-2, a'.sub.2-1 and a'.sub.2-2. By using a clock pulse train having a bit rate higher than said bit clock bc by three times, these signals a'.sub.1-1, a'.sub.1-2, a'.sub.2-1 and a'.sub.2-2 are read out sequentially from said serial output terminal.
For example, in case of 96 channels of audio signals, the audio signals of the 1st to 48th channels are pulse-code-modulated and multiplexed in time division by said first PCM-TDM processor 91. In this example, PCM processing is carried out by a sampling frequency of 10.5 KHz, 256 quantizing levels (8 digit numbers) and frame period pulse of 8 digits, and a pulse repetition frequency obtained by multiplexing 50 channels of audio signals in time division is 4.116 MHz.
The remaining audio signals 49th to 96th channels are also processed by said second PCM-TDM processor 93 in a similar way. The two series of PCM pulse trains thus produced are arranged as shown in FIG. 7. As the sampling frequency of this example is chosen to be 10.5 KHz which is equal to 2/3 the time of the horizontal synchronizing frequency 15.75 KHz of the television signal, one television picture, i.e., one television frame (1F=525 scanning lines), is equal to 350f (f is a PCM frame). Accordingly, the audio signal corresponding to three television frames (3F) is equal to 1050f of PCM frames. The former PCM frames 700f are allotted to the signal a.sub.1-1 or a.sub.2-1 and the remaining latter frames 350f are allotted to the signal a.sub.1-2 or a.sub.2-2.
As to pulse arrangement within 1f of the PCM-TDM signal, as shown in FIG. 7b, the 1st to 8th pulses are allotted to PCM frame synchronization, 9th to 16th pulses to the quantized pulse group corresponding to the first audio signal, 17th to 24th pulses to that corresponding to the second audio signal, and 384th to 392nd pulses to that corresponding to the 48th audio signal. The same is applicable to the 49th to 96th audio signals. The above mentioned signals are derived from said PCM-TDM processors 91 and 93 of FIG. 6.
The embodiment of said PCM-TDM processor will be explained in detail with reference to FIG. 8. In FIG. 8, reference numerals 113-1 to 113-48 denote audio input signal terminals, and 115 denotes a selecting switch for selecting one of said terminals 113-1 to 113-48. The switch 115 is driven by an audio sampling signal S so as to sequentially select one of said input terminals 113 and to sample the audio input signal sequentially. The whole selecting period of the switch 115 is equal to the inverse number of the sampling frequency of the audio signal, i.e., (1/10.5).times.10.sup..sup.-3 sec, so that the rate of changing each input terminal by switch 115 is ##EQU1## The sampled signal is amplified by an amplifier 117. The amplified output is applied to a sample hold circuit composed of a switch 119 and a capacitor 121. The continuous analog output signal from the amplifier 117 is sampled by the switch 119 and the thus sampled signal is held (as a constant value) during a given period by the capacitor 121. The signal held by the capacitor 121 is applied to a differential amplifier 123 in which said sample-hold signal and the output from a weighting resistor circuit 125 are differentially amplified. The differential output signal from the amplifier 123 is applied to a polarity decision circuit 127. The output of this circuit 127 is supplied to a PCM output terminal 129 and to a register 131 for storing the output PCM signal temporarily. The register outputs are supplied to a switch group 133 and control this switch group. Said weighting resistor circuit has many weighting resistors 125-1 to 125-8, each of which has a resistance value of R, 2R, 4R, . . . 128R, respectively, and is connected to said switch group 133. To this switch group 133 is supplied a clock signal bc.
When the sample-hold signal is applied to the differential amplifier 123 for the first time, no output signal is obtained from the PCM output terminal 129. Accordingly, no signal is stored into the register 131, so that no signal is applied to the switch group 133. As the switch group 133 does not operate, the output of the weighting resistor circuit 125 is zero potential. In such condition, the differential amplifier 123 operates only as a usual amplifier, so that its output signal is proportional to its input signal. This output signal is supplied to the polarity decision circuit 127 in which it is decided whether this output signal is large or small relative to a given decision level. The decision output thus obtained is the MSD (most significant digit) of the PCM output signal. This decision output signal is stored into the register 131. The PCM output signal stored for the first time, i.e., the MSD signal is applied through the first output 131-1 to the switch group 133 at the timing of the bit clock bc. If MSD="1", a constant voltage output is produced from the switch group 133 and is applied to said differential amplifier 123 by the resistor 125-1 of the weighting resistor circuit 125. If MSD="0", the output of the weighting resistor circuit 125 remains zero potential. Here, for the description hereinafter, MSD assumes to be 1. The constant voltage of the output of the circuit 125 can be varied by the voltage supplied from the switch group 133 and in this case, the constant voltage is present to be a half of the maximum value of the output of said capacitor 121. Then the differential amplifier 123 amplifies the difference of two inputs, so that this amplifier 123 produces a voltage shifted (or decreased) by a half of the maximum level. This voltage is compared with the decision level in the circuit 127 so as to produce a second PCM output, i.e., a second significant digit. This PCM output is stored in said register 131. This stored PCM output is applied through the second output 131-2 to the switch group 133 so as to produce a constant voltage by the resistor 125-2. This resistor 125-2 has a resistance value 2R which is larger than that of the resistor 125-1, so that the voltage produced by the resistor 125-2 is a half of the voltage produced by the resistor 125-1.
If the second PCM output is also 1, the voltage obtained from the weighting resistor circuit 125 becomes three-fourths (1/2 + 1/4 = 3/4) of the maximum voltage held by said capacitor 121. This newly obtained voltage is applied to the differential amplifier 123 and subsequently to the polarity decision circuit 127 so as to decide the PCM sign. The same process is repeated until the register 131 is fully stored. After fully storing, PCM processing of one audio signal is completed. During this PCM processing the signal held by said capacitor 121 is required to be constant. Otherwise, the reference level of the early decision differs from that of the last decision, and this difference causes signal distortion. Hence, the signal from the capacitor 121 must be held at a constant value during PCM processing of one audio signal.
After the above PCM processing, said selecting switch 115 is changed to the next input terminal 113-2, and the audio signal of the second channel is passed to the amplifier 117. The output signal of the amplifier 117 is processed in the same way as above.
The same is applied to all of the 48 channels of audio signals by sequentially changing the selecting switch 115.
For the above switches, amplifier and so on, usual integrated circuits can be employed, such as DG506 for the switch 115, G150 for the switch 119, DG501 for the switch 133, .mu.A709 for the amplifiers 117 and 123, .mu.A710 for the polarity decision circuit 127, 9300 for the register 131, and so on.
In FIG. 6, the AND gates 95, 97, 99, 101 divide the signals a.sub.1 and a.sub.2 (shown in FIG. 5c) to the parts a.sub.1-1, a.sub.1-2, a.sub.2-1 and a.sub.2-2 and rearrange these parts as shown in FIG. 5c. That is, the part a.sub.1-1 passed through the gate 95 is delayed by two frame periods (2F=2/30 sec.) by the delay circuit 103 so as to produce the signal A (a'.sub.1-1). The part a.sub.2-1 passed through the gate 101 is delayed by one frame period by the delay circuit 105 for producing the signal C (a'.sub.2-1). The part a.sub.1-2 passed through the gate 97 and the part a.sub.2-2 passed through the gate 99 are combined by the mixing circuit 107 to produce the signal B. By shifting the parts a.sub.1-2 and a.sub.2-2 by one frame period which is equal to the time length of the part a.sub.1-2, the parts a.sub.1-2 and a.sub.2-1 can be connected without any time gap or without overlapping. These three signals A, B and C are processed only by delaying and rearranging, so that the pulse repetition frequency of these signals A, B and C is not varied and maintains 4.116 MHz. The gate pulses supplied to said AND gates 95, 97, 99 and 101 are shown in FIGS. 9a-9f.
These three signals A, B and C are applied to the time division multiplexer 109 in which the pulse width of each signal is compressed to one third of the original width and two thirds thereof is kept blank and reserved for the remaining two signals which are interposed into this blank period. By this compressing process, the pulse repetition frequency becomes 12.348 MHz which is a value of three times of said frequency 4.116 MHz. This process is shown in FIGS. 10a-10c. As clearly shown in FIGS. 10a-10c, the pulses of said three pulse signal trains, A, B and C are extracted from these pulse trains in time sequence of A, B and C, such as A.sub.1, B.sub.1, C.sub.1, A.sub.2, B.sub.2, C.sub.2 . . . , and are arranged in series. The above process for obtaining the time division multiplexed output signal is clear from the pulse arrangement of FIGS. 11a-11e.
FIG. 11a shows two series of PCM-TDM signals a.sub.1 and a.sub.2 produced from said PCM-TDM processors 91 and 93. FIG. 11b shows said three signals A, B and C applied to said time division multiplexer. The signal A, B or C has 700 PCM frames (1f-700f), one of which has, as shown in FIG. 11c, three synchronizing signals, S.sub.A, S.sub.B and S.sub.C occupying one PCM channel and audio PCM signals each of which has 48 PCM channels 1-1, 2-1 . . . 48-1 . . . 1-701, 2-701 . . . 48-701, 49-1, 50-1 . . . 96-1, 49-701, 50-701 . . . 96-701. The PCM channel of FIG. 11c has eight bits as shown in FIG. 11d. The signals A, B and C thus composed are multiplexed in time division by the time division multiplexer 109 so as to derive the signal shown in FIG. 11e in which the respective bits of the signals A, B and C are alternately adjacent to each other in time division.
The multiplexed signal from the multiplexer 109 is converted to the four-level signal by the two-four level converter 111. The reason for converting the level of the PCM pulse signal will be explained hereinafter.
The output pulse produced from the TDM processor 109 is a binary form, so that the pulse repetition frequency becomes higher, for example 12.348 MHz in the case of FIG. 11 and that transmission frequency band becomes broader as the information to be transmitted increases. Accordingly, the binary pulse form is not suitably applied to the television broadcasting system having a given restricted transmission frequency band. Considering the above, in order to improve the amount of the information to be transmitted, the multilevel pulse transmission system can be utilized. In case of a four level pulse, the pulse repetition frequency can be reduced to a half of 12.348 MHz, i.e., 6.174 MHz.
In order to form the four-level pulse, two continuous binary pulse trains or two independently formed binary pulse trains are suitably combined. In FIG. 11, the pulse train of 12.348 MHz has been formed, so that the pulses are alternately extracted so as to combine with the remaining pulses.
In the two-four level converter 111 in FIG. 6, the pulse amplitude of one of said two pulse series is decreased to be a half of the pulse amplitude of the other and thereafter the two pulse series are added to one another in synchronism so as to obtain the four-level pulse. The pulse repetition frequency of said four-level pulse is 6.174 MHz.
The one PCM frame (1f) signal in the combined signal in FIG. 11 has three multiplexed portions of 48 channels of the audio information signals each of which is quantized in eight bits for one sample signal and three multiplexed portions of eight bits relating to the synchronizing signal portion, so that the 1f signal is totally composed of 600 bits of information.
In a practical transmitting signal, the audio information signal in the 1f signal is the same as the above, while the synchronizing signal portion is composed of 48 bits, i.e., twice the bits of the above bits.
Thus, said 1f signal has the total bits of 624. According to the monochrome television standard in which the horizontal synchronizing frequency is 15.75 KHz, said pulse repetition frequencies 12.348 MHz and 6.174 MHz are respectively changed to 13.104 MHz and 6.552 MHz. According to the present color television standard in which the horizontal synchronizing frequency is 15.734 KHz, said frequencies 12.348 MHz and 6.174 MHz are respectively changed to 13.0909 MHz and 6.5454 MHz. The following explanation will be in conformity with the monochrome television standard.
The apparatus for reproducing the original audio signal from the transmitted signal as shown in FIG. 5d and produced by the arrangement of FIG. 6 will now be shown in FIG. 12. This apparatus corresponds to the audio reallocation processor 81 in FIG. 3.
A four-two level converter 135 receives the transmitted four-level PCM signal and converts it to a two-level signal. The converted two-level signal is applied to a pulse rate converter 137 in which the received signals A, B and C are divided to one another again and the pulse rate of these signals are reduced to a third of the received one. The output signal from said converter 137 is applied to a channel gate 139 which is controlled by a channel selector 141 so as to extract the signal contained in a time slot corresponding to a desired channel. The gated signal from this gate is discriminated whether this gated signal corresponds to the signal A, B or C. In case of this signal corresponding to the signal A or C, this gated signal is directly supplied to a mixing circuit 143 without passing through delay circuits 145 and 147. If the gated signal corresponds to the signal B, this signal is discriminated whether it corresponds to the signal a'.sub.1-2 contained in the former half of the audio transmission period or to the signal a'.sub.2-2 related to the latter half thereof. In case of corresponding to the signal a'.sub.1-2, the gated signal is applied to the two-frame-period delay circuit 147. In case of corresponding to the signal a'.sub.2-2, the gated signal is applied to the one-frame-period delay circuit 145. The outputs of these delay circuits 145 and 147 are connected to the mixing circuit 143. In this way, by the process already explained with reference to FIG. 4d, the original signal a.sub.1 or a.sub.2 is reproduced from the output terminal of said mixing circuit 143. As the reproduced signals a.sub.1 and a.sub.2 are still PCM digital signals, these signals are converted to analog signals by a digital-to-analog converter so as to reproduce a usual audio signal.
In the above-mentioned still picture-audio PCM multiplexing transmission system, the delay lines are utilized to convert the plurality of continuous signals, i.e., the original audio signals to the transmitting signals which are the TDM signals in the form of four-level signals. In such a case, it is necessary that the plurality of continuous signals such as 96 channels of original audio signals are applied to the plurality of the corresponding input terminals in parallel and simultaneously. Accordingly, the above transmission system is adopted to the purpose of transmitting much information in multiplexed form, but this system has a drawback in that this system is less flexible in the point of input signals to be applied because it is not possible to apply input signals independently to one another.